Example Maven Configuration : Installing a package

(installing a package) pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.mattamorphic.maven.gpr</groupId>
    <artifactId>maven-install-test</artifactId>
    <version>1.0.0</version>

    <dependencies>
        <dependency>
            <groupId>com.mattamorphic</groupId>
            <artifactId>maven-assembly-example</artifactId>
            <version>0.2</version>
        </dependency>
    </dependencies>

</project>

(publishing a package) pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
                    http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.mattamorphic</groupId>
    <artifactId>maven-assembly-example</artifactId>
    <version>0.2</version>

    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
      <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-lang3</artifactId>
        <version>3.0</version>
      </dependency>
    </dependencies>

    <distributionManagement>
        <repository>
            <id>github</id>
            <name>GitHub mattamorphic Apache Maven Packages</name>
            <url>https://maven.pkg.github.com/mattamorphic/maven-assembly-example/</url>
        </repository>
    </distributionManagement>

    <build>
      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <configuration>
            <source>7</source>
            <target>7</target>
          </configuration>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-jar-plugin</artifactId>
          <version>2.4</version>
          <configuration>
            <archive>
              <manifest>
                <addClasspath>true</addClasspath>
                <classpathPrefix>lib</classpathPrefix>
                <mainClass>com.sample.Main</mainClass>
              </manifest>
            </archive>
          </configuration>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-assembly-plugin</artifactId>
          <executions>
            <execution>
              <phase>package</phase>
              <goals>
                <goal>single</goal>
              </goals>
              <configuration>
                <appendAssemblyId>false</appendAssemblyId>
                <descriptors>
                  <descriptor>src/com/assembly/zip.xml</descriptor>
                </descriptors>
              </configuration>
            </execution>
          </executions>
      </plugin>
    </plugins>
  </build>
</project>

settings.xml

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
                      http://maven.apache.org/xsd/settings-1.0.0.xsd">

  <activeProfiles>
    <activeProfile>github</activeProfile>
  </activeProfiles>

  <profiles>
    <profile>
      <id>github</id>
      <repositories>
        <repository>
          <id>central</id>
          <url>https://repo1.maven.org/maven2</url>
          <releases><enabled>true</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </repository>
        <repository>
          <id>github</id>
          <name>GitHub mattamorphic Apache Maven Packages</name>
          <url>https://maven.pkg.github.com/mattamorphic/maven-assembly-example</url>
        </repository>
        <repository>
          <id>github</id>
          <name>GitHub mattamorphic Apache Maven Packages</name>
          <url>https://maven.pkg.github.com/mattamorphic/test-service</url>
        </repository>
       </repositories>
    </profile>
  </profiles>

  <servers>
    <server>
      <id>github</id>
      <username>mattamorphic</username>
      <password>TOKEN</password>
    </server>
  </servers>
</settings>

workflow.yml

name: Publish Maven package using Actions

on:
  push: 
    branches:
    - master
    paths:
    - 'mypackage/*'
    - '.github/workflows/workflow.yml'

jobs:
  build:

    runs-on: ubuntu-latest
    
    steps:
    - uses: actions/checkout@v1
    - name: Setup Java
      uses: actions/setup-java@v1
      with:
        java-version: '9.0.4'
    - name: Add GPR token to template settings.xml
      run: sed -i -e 's/TOKEN/'$GITHUB_TOKEN'/g' mypackage/settings.xml
      env:
          GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}
    - name: Create the package
      run: |
           cd mypackage/
           mvn package --settings settings.xml
    - name: Publish the package
      run: |
           cd mypackage/
           mvn deploy --settings settings.xml

If the Maven repository was hosted at https://maven.pkg.github.com/<username> rather than https://maven.pkg.github.com/<username>/<repo> it would be much more practical for users with a large number of libraries, else we will end up having to list a huge number of Maven repositories - and Maven checks every single one until it finds a package.

fully agree with harmanpa.. We have 90+ maven repositories hosted on Github in our organization. we've abandoned migrating to Github Package Registry for this reason alone.. We are definitely not going to update the settings.xml for all developers for 90+ repositories and having to update it every time we have a new repository. The repositories should be hosted at the organization level.